Not Applicable
The present invention is directed generally to optical transmission networks. More particularly, the invention relates to optical transmission systems including protection capability for use in optical communication networks.
Communications transport systems are used to transport information over a substantial portion of the world. This extensive communication access requires enormous amounts of equipment to provide the necessary infrastructure for the systems. In addition, much of the equipment and almost all of the transport media is remotely located and necessarily exposed to the environment.
In view of the necessary exposure of transmission systems to uncontrolled environments, it is not uncommon for failures to occur along a transmission path. However, if communication systems are to be effective it is necessary to have a high degree of reliability in the system. Thus, communication systems must provide for protection of the information being transmitted through the systems, as well as for restoration of failed links in the system.
The reliability of service provided by a transmission system is inversely proportional to the frequency of failures in the transmission system. One of the most common failures in fiber optic transmission networks is a fiber break. When a fiber break or other failure occurs in a transmission link, the traffic intended to pass through the link must be rerouted through another path until the link is restored. Another common source of failures in optical transmission network is an equipment failure. The amount of traffic that is lost upon an equipment failure depends upon the particular piece of failed equipment in the network. For example, in most, if not all, currently available fiber optic transport networks, a line amplifier failure will result in a complete loss of traffic traveling through an optical link containing the failed line amplifier. Whereas, a transmitter or a receiver failure will generally result only in the loss of the wavelengths associated with the failed transmitter or receiver.
Despite the persistent hazards of uncontrolled exposure to environmental conditions and inevitable equipment failures, it is imperative that communications service providers supply high quality service. Therefore, service providers have developed protection schemes to provide automatic traffic restoration upon a transmission link failure and have required redundant equipment systems to decrease the effective failure rate of the link.
Protection schemes generally are categorized based on the relationship of a working channel and a protection channel and the topology of the network. If information is transmitted through the network on both a working channel and a protection channel, the schemes are referred to as providing one plus one (xe2x80x9c1+1xe2x80x9d) protection. Upon a failure of the working channel, the network switches to the protection channel. If information is switched from a working channel to protection channel or working path to a protection path when a failure occurs, the schemes are referred to as one for one (xe2x80x9c1:1xe2x80x9d) protection schemes. More generally, M protection channels or paths can be shared between N working channels or paths, which is generally designated as M:N protection. Similarly, M protection channels can carry the same information as the working channel to provide 1+M protection.
Protection schemes can be implemented using various multiple fiber switching topologies, which generally fall into two distinct classes. The first class of protection schemes is referred to as Unidirectional Path-Switched Ring (xe2x80x9cUPSRxe2x80x9d) in SONET, or Dedicated Protection Ring (xe2x80x9cDPRingxe2x80x9d) in SDH. The second class is known as Bi-directional Line-Switched Ring (xe2x80x9cBLSRxe2x80x9d) in SONET, or Multiplex Section-Shared Protection Ring (xe2x80x9cMS-SPRingxe2x80x9d) in SDH. UPSR and BLSR schemes can implemented using either electrical or optical switching, O-BLSR and O-UPSR.
In UPSR schemes, working fiber paths for each direction connecting two nodes are on the same fiber ring and the protection paths for each direction are on a different fiber ring. Traffic from an origination node is sent along both the working and protection paths to a destination node. In the event of a failure of the working fiber path using UPSR protection, the destination node electrically or optically switches to the protection path to receive the traffic.
In BLSR schemes, transmission capacity of the ring fibers is divided between working and protection capacities, which carry traffic in opposite directions. Communications traffic is sent between origination and destination nodes using the working capacity of the ring.
When a failure occurs, the nodes immediately adjacent to and on both sides of the failure switch the traffic to the protection capacity on a different fiber, which propagates in the opposite direction. Traffic is looped back around the failure by the two proximate switches using the protection fiber generally without further reconfiguration of the system. In transoceanic BLSR applications, additional switching may be performed to minimize the additional distance traveled by the rerouted traffic.
BLSR is available in 2-fiber and 4-fiber implementations. In 4-fiber implementations, a protection fiber is provided for each working fiber and traffic is rerouted by switching between the working and protection fibers. In the 2-fiber implementations, the working and protection capacities are time division multiplexed (xe2x80x9cTDMxe2x80x9d) on the same wavelengths, when electrical BLSR switching is performed. When 2 fiber, optical BLSR switching is performed, wavelengths are allocated to working channels on one fiber and to protection channel on the other fiber to allow the wavelength to be multiplexed.
Also, some BLSR schemes allow lower priority traffic to be transported using the protection capacity to increase the system capacity and utilization efficiency during normal operation. If protection switching is necessary, the lower priority traffic is dropped in favor of protecting the higher priority traffic.
As the demand for transmission capacity continues to grow, there is an increasing need to efficiently use the available transmission capacity and protect the information being transported through the systems. The increased amount of traffic being carried on each fiber places increased importance on the ability to effectively protect the information, because each failure results in higher revenue losses for service providers. Accordingly, there is a need for optical transmission systems and protection schemes that provide effective protection with increasing wavelength efficiencies for use in long distance communication systems.
The present invention addresses the need for higher reliability optical transmission systems, apparatuses, and methods. Optical systems of the present invention are configured in optical networks including a plurality of optical switch nodes interconnected by a plurality of optical transmission fibers, or other waveguides. The transmission fibers provide working and/or protection capacity for information, or communications traffic, being transmitted through the network.
In various embodiments of the network, multiple diverse, working routes are provided on a single fiber path interconnecting a plurality of the switch nodes. Shared protection for the multiple, diverse working routes can then be provided using a common protection fiber or path in the system.
The switch nodes include optical switch configured to provide various levels of optical switching depending upon the network configuration. For example, line switches as well as wavelength selective optical cross-connects and routers can be deployed as optical switches in the switch nodes. The optical switches are configured to introduce, remove, and/or pass various signal wavelengths through the working and protection paths. The switch nodes will function differently depending upon whether the node is an origination, destination, or intermediate switch node with respect to an individual signal wavelength or group of wavelengths. The optical systems can be further configured to carry lower priority traffic on the protection fibers or wavelengths during normal operation to increase the overall normal operating capacity of the system.
The use of optical switching at the switch nodes along the working and protection paths connecting signal wavelength origination and destination nodes decreases the amount of redundancy necessary for optical protection. Accordingly, the present invention addresses the aforementioned concerns by providing optical systems apparatuses, and methods having increasingly flexible protection schemes. These advantages and others will become apparent from the following detailed description.